In an internal combustion engine, a supply of engine lubricant, such as petroleum oil, is provided in an oil pan at the bottom of the engine. During operation of the engine, a pump is used to carry the oil from the pan up into the working portions of the engine in order to lubricate the engine's moving parts. As oil is continuously supplied to these moving parts, excess oil drains back to the oil pan through various paths by the operation of gravity. In this way, oil is continuously circulated through the engine while it is operating.
Referring to FIG. 1, there is illustrated a camshaft compartment of a prior art internal combustion engine, the camshaft compartment being indicated generally at 10. The compartment 10 includes end walls 12 and 24, as well as dividing walls 14-22. Each of the walls 12-24 include a respective cam journal 26 formed therethrough. A camshaft 28 (shown in phantom in FIG. 2) is rotatably supported by the cam journals 26.
Oil is supplied by the engine oil pump to the camshaft 28 in order to lubricate the camshaft 28 as it rotates in the cam journals 26. During this process oil is continuously drained off of the camshaft 28 into the bottom of the compartment, 10. This excess oil must be drained back into the oil pan so that it may once again be pumped into the lubrication circuit. The compartment 10 includes a plurality of large drainback holes 30 which allow the excess oil to drain back to the oil pan. As best illustrated in FIG. 2, the walls 14, 18 and 22 do not extend all the way to the bottom of the compartment 10, thereby forming three separate chambers 19, 21 and 23, each chamber having two drainback holes 30. Because the drainback holes 30 are large enough to allow a significant quantity of oil to pass therethrough, no appreciable quantity of oil remains in the compartment 10 during engine operation. All excess oil is immediately returned to the oil pan.
Consumers who purchase internal combustion engines desire engines which contain a large volume of oil. The larger the oil volume, the longer the drain interval between required oil changes, and therefore the engine exhibits lower maintenance costs. The longer drain interval results from a lower duty cycle for each particular oil molecule when the total quantity of oil molecules is increased. However, if the oil pan is simply tilled with more oil, the fuel economy of the engine is lowered. This results from the fact that the oil pan is situated immediately below the engine crankshaft. As the level of oil in the pan is increased, the rotating crankshaft interacts with the oil, causing drag on the crankshaft and windage losses which lower the efficiency of the engine. It is not feasible to provide a larger oil volume by simply increasing the size of the oil pan. This is because consumers also desire a small engine package size.
In the past, therefore, engine designers have been forced to make trade-offs between oil volume, fuel economy and package size. Such trade-offs have been thought to be necessary when more oil is required, but more oil can't be added to the pan and the pan can't, be made larger. There is therebefore a need in the prior art for a way to increase engine oil volume without lowering engine fuel economy or increasing engine package size. The present invention is directed toward meeting this need.